Developmental neurogenetic diseases can only be studied, and potentially treated, once systems to predictably deliver and express genes in neuronal cells are developed. We have utilized herpes simplex virus (HSV) as a vector for expressing genes in neuronal cells. This human DNA virus, for which about 90 percent of the U.S. population is seropositive, forms latent infections which persist for the lifetime of the individual. Using HSV derived vectors, we will study the nervous system component of lysosomal storage disease. Lysosomal storage in neurons results in severe mental retardation in most children with these diseases. Specifically, we will use a Beta-glucuronidase-negative-mouse (gusmps/gusmps), with mucopolysaccharidosis (MPS) type VII (Sly disease) as an animal model. During the previous grant period we demonstrated that a recombinant HSV vector with a Beta-glucuronidase gene under control of the only viral promoter, that is active during latency (LAT promoter), could move from the periphery to the central nervous system. By using this promoter we achieved long term expression of the corrected gene in the nervous system of diseased mice. We noted several problems, including lower than expected numbers of latently infected cells, discordant enzyme levels relative to mRNA levels, and hightened pathogenesis in mutant compared to normal mice. We have developed vector strains of HSV suitable for direct intercranial inoculation into CNS and examined their pathogenesis. We now wish to continue our studies by examining the factors that increase GUSB activity in neuronal cells, and increase the number of corrected cells, to bring vector correction to a level that will change the clinical disease. Specifically, this will be achieved by examining various chimeric LAT-GUSB genes for their ability to express both at the RNA and the translational level in the context of latent HSV. The goal of these studies is to address the problem of treatment of neurogenetic diseases by developing a method of expressing genes in the nervous system in vivo using a ubiquitous human virus. These studies will also provide a method for studying gene regulation in neuronal cells in vivo using the state of the art techniques of molecular biology.